Developmental and environmental modulation of fecal thyroid hormone levels in wild Assamese macaques (Macaca assamensis)

• Published in: American journal of primatology 2023-09, Vol.85 (9), p.e23530-n/a
• Main Authors: Behringer, Verena, Heistermann, Michael, Malaivijitnond, Suchinda, Schülke, Oliver, Ostner, Julia
• Format: Article
• Language: English
• Subjects: Change agents; Developmental processes; Developmental stages; Environmental aspects; Environmental changes; Environmental conditions; Environmental factors; Feasibility; Feasibility studies; fecal thyroid hormones; Feces; Food availability; Glucocorticoids; Hormone levels; Hormones; Immunomodulation; Infants; Macaca assamensis; Measurement; Metabolism; Modulators; noninvasive measurement; primate development; Primates; Stress (physiology); Stress response; Thyroid; Thyroid gland; Thyroid hormones; Triiodothyronine; Wildlife; wildlife endocrinology; Wildlife refuges; Zoo animals
• ISSN: 0275-2565; 1098-2345
• DOI: 10.1002/ajp.23530

Thyroid hormones are key modulators of development, as well as mediators of environmental conditions, by regulating developmental processes and metabolism in primates. Hormone measurement in noninvasively collected samples, that is, feces and urine, is a valuable tool for studying the endocrine function of wildlife, and recent studies have demonstrated the feasibility of measuring thyroid hormones in fecal samples of zoo‐housed and wild nonhuman primates. Our study aimed to (i) validate the measurement of immunoreactive fecal total triiodothyronine (IF‐T3) in wild Assamese macaques (Macaca assamensis) and (ii) to investigate its developmental changes and its response to environmental changes, including stress responses, in immature individuals. Fecal samples and environmental parameters were collected from individuals of three social groups of wild Assamese macaques living at Phu Khieo Wildlife Sanctuary, Northeastern Thailand. Our study confirmed the methodological feasibility and biological validity of measuring IF‐T3 in this population. Specifically, the biological validation demonstrated higher IF‐T3 levels in immatures compared to adults, and higher levels in females during late gestation compared to the preconception stage. Our analysis of IF‐T3 levels in developing immature macaques revealed a significant increase with age. Furthermore, we found a positive association between IF‐T3 and immunoreactive fecal glucocorticoid levels, an indicator of the physiological stress response. Neither minimum temperature nor fruit abundance predicted variation in IF‐T3 levels in the immatures. Our findings indicate the possibility for differing effects of climatic factors and food availability on thyroid hormone level changes in immature versus adult animals and in wild compared to experimental conditions. Overall, our study provides the basis for further investigations into the role of thyroid hormones in shaping species‐specific traits, growth, and overall primate development. Research highlights Total triiodothyronine (T3) levels can be measured noninvasively in the feces of wild Assamese macaques. Total T3 levels are higher in juveniles compared to infants and are positively associated with glucocorticoid levels. Environmental factors did not affect total T3 profiles in immature macaques, highlighting potential developmental effects on thyroid hormone regulation.